One board will always bring compromise. His top end is 20-25, so one assumes that the rest of the time, will be at lower wind speeds.
Racers will know its "go big or go home" and I think Naish once said "there's worse things than being overpowered".
Even if he is not racing, he may well want to be planing for the maximum amount of time and an IS96 with 7.8 & 6.3 wont achieve that. I agree the 133 may be slightly big but he needs to be closer to 133 than 96.

Brazilian pro racer Wilhelm Schurmann aced this years Highland Spring HIHO event. The top ranked Formula racer won all seven races in the events 6-day schedule.
“Schurmann made it look easy,” said race director Simon Woods. “He was first off the line at every start, and always first to finish.”
Schurmann sailed a 10.0 V8 sail and used the stock Techno 2 race fin
throughout the event. “It was the perfect set-up for the 15-18 knot winds we had all week”, he said. “I was always set-up just right- fast and in-control on the long inter-island legs.”